8

4872A–CORD–08/05

U4091BM-R

7.

Clock Output Divider Adjustment

The pin OSCOUT is a clock output which is derived from the crystal oscillator. It can be used to

drive a microcontroller or another remote component and thereby reduces the number of crys-

tals required. The oscillator frequency can be divided by 1, 8, 16, or 32. During power-on reset,

the divider will be reset to 1 until it is changed by setting the serial bus.

8.

Serial Bus Interface

The circuit is controlled by an external microcontroller through the serial bus.

The serial bus is a bi-directional system consisting of a single-directional clock line (SCL) which

is always driven by the microcontroller, and a bi-directional data-signal line. It is driven by the

microcontroller as well as by the U4091BM-R (see Figure 20-1 on page 37).

The serial bus requires external pull-up resistors as only pull-down transistors (pin SDA) are

integrated.

8.1

WRITE

The data is a 12-bit word:

A0-A3: address of the destination register (0 to 15)

D0-D7: content of the register

The data line must be stable when the clock is high. Data must be shifted serially. After 12 clock

periods, the write indication is sent. Then, the transfer to the destination register is (internally)

generated by a strobe signal transition of the data line when the clock is high.

8.2

READ

There is a normal and a fast-read cycle.

In the normal read cycle, the microcontroller sends a 4-bit address followed by the read indica-

tor, then an 8-bit word is read out. The U4091BM-R drives the data line.

The fast read cycle is indicated by a strobe signal. With the following two clocks the U4091BM-R

reads out the status bits RFDO and LIDET which indicate that a ringing signal or a line signal is

present (see Figure 10-1 on page 11, Figure 10-2 on page 11 and Figure 10-3 on page 11).

Table 6-1.

Threshold Level

RINGTH[0:3]

V

RING

07V

15

22V

Step

1V

Table 7-1.

Clock Output

CLK[0:1]

Divider

Frequency

0

1

3.58 MHz

1

8

447 kHz

2

16

224 kHz

3

32

112 kHz